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I. program chips
1.EPROM generally not damaged. chips need ultraviolet light to clean to get rid of the program, it will not damage in the test program. information: results from chip-making materials, along with the passage of time (year long), even without has the potential to damage (mainly refers to the program.) so as to give the backup.
2.EEPROM,SPROM, and with battery of RAM chip, are very easy damage program. This class chip whether in using < test instrument > for VI curve scan Hou, whether on damage has program, also not has findings. Nevertheless, colleagues are in encountered this situation Shi, also is carefully for wonderful. author had do had times test, may big of reasons is: maintenance tool (as test instrument, iron,) of shell leakage due to.
3. for the battery on the circuit board chip do not easily be removed from the Board.
II. reset circuit
1. for repairs on circuit boards when there is a large scale integrated circuits, reset problems needing attention.
2. prior to the test the best back on the device, repeated opening, turn off the machine to give it a try ... and press the reset button a few times.
III. functions and parameters
1.< tester > detection of devices can only reflect the cutoff region, enlarged and saturation zone. but cannot detect the frequency of high and low and speed of specific values, and so on.
2. for TTL chips, similarly, can only know there are high and low level of output changes. and unable to detect the speed of its rise and fall along.
IV. the crystal oscillator
1. normally only use oscilloscope (crystal oscillator power requirements) or frequency meter test, meter cannot measure or the substitution method is used.
2. Crystal common faults are: a. internal leakage, b. internal open circuit c. metamorphic frequency offset d. peripheral connected capacitor leakage. leakage phenomenon, with < tester > VI curves can be measured.
3. the whole Board testing can be used two ways: a. testing near Crystal chips around, you don't through. b. in addition to Crystal did not find other points of failure.
4. common 2 Crystal: a. feet. b. four feet, the 2nd foot plus power supply, pay attention not to short circuit
V. distribution of symptoms
1. Circuit Board parts of incomplete statistics: 1) chip damage 30%, 2) discrete component damage to 30%,
3) connections (PCB Board with copper) break 30%, 4) damaged or lost 10% (rising).
2. from the foregoing, links and procedures when repairing circuit boards appear when there is a problem, and no good boards, is not familiar with the line and cannot find the original program. This Board fixed the possibility is unlikely.
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